Savanna chimpanzees suffer from dehydration, heat stress: Study

"This underlines the importance of adaptations for overcoming or avoiding thermoregulatory stress in our own evolutionary history," said anthropologist Erin Wessling.

During the dry season in Fongoli, Senegal, temperatures regularly rise above 37 degrees Celsius, triggering heat stress and dehydration among chimps living in the savanna. Photo Erin Wessling/MPG

May 15 (UPI) -- New research suggests chimpanzees living among the savanna near Fongoli, a rural community in Senegal, are affected by heat stress.

When scientists with the Max Planck Institute for Evolutionary Anthropology collected and analyzed urine samples from the Fongoli chimpanzees, they found high levels of creatinine and cortisol, biomarkers revealing elevated levels of heat stress and dehydration.

"The weather at Fongoli can be brutal, where the average maximum temperature is over 37 degrees Celsius, and periods go by each year when rain doesn't fall for over seven months," anthropologist Erin Wessling said in a news release.

Researchers also found levels of c-peptide -- an insulin peptide linked with energetic status -- varied according to food availability during the study period, but that chimpanzees living among the savanna weren't experiencing energetic stress.

"This really supports the idea that the strongest challenges of habitats like these savanna, savanna-woodland environments are staying adequately hydrated and cool," said Wessling.

Anthropologists have argued that climatic change, triggering the decline of forests and an expansion of savannas across Africa, played an important role in the evolution of early humans.

"If we are thought to have evolved in similar habitats, then this underlines the importance of adaptations for overcoming or avoiding thermoregulatory stress in our own evolutionary history," Wessling said. "As a next step, it would then be important to show that these stresses are not only important, but also unique to these types of habitats."

In a follow-up study, Wessling and her colleagues analyzed biomarkers in the urine of chimpanzees living in Tai National Park, a lowland rainforest in the Ivory Coast. Their findings showed the apes experienced no thermoregulatory stress, as temperatures are relatively cool.

But the data also showed chimps living in the rainforest experience more energetic stress despite an abundance of food. The findings suggest savanna chimps have begun to adapt to the challenges of their more hostile environs, adopting a more diversified diet.

If the transition from ape to human began on the savanna, researchers believe diet and thermoregulatory adaptations were key. The latest research -- detailed in a pair of papers published this week in the journal Frontiers in Ecology and Evolution -- suggests those adaptations can be observed among the chimps of Senegal.

"The Fongoli chimpanzees, for example, have demonstrated several extraordinary behaviors suspected for dealing with the savanna heat, such as cave use, sitting in pools, and nocturnal activity," said Wessling. "However, despite these behaviors, they still show signs of dehydration and thermoregulatory stress, suggesting more dramatic adaptations, such as anatomical changes, may be needed to completely evade such pressures."